Disarticulation is the amputation of a limb through a joint. Often, disarticulation occurs without the cutting of bone. For example, hip disarticulation is an amputation through the hip joint, removing the entire leg at the hip joint. Shoulder disarticulation is an amputation through the shoulder joint, removing the entire arm at the shoulder joint. Disarticulation is also known as exarticulation.
Amputees who have undergone either disarticulation often wish to be fitted with prosthetic equipment that will allow them to replicate at least a portion of the function of the missing limb.
Unlike in a transhumeral amputation or transfemoral amputation, where the shoulder and hip are left intact and the patient has a humeral/femoral stump to attach an external prosthesis to, in a shoulder or hip disarticulation the patient has no residual limb stump extending from the scapula or pelvis to be received in the socket of an external prosthesis (exoprosthesis) and to provide a stable anchoring point for the prosthesis. In a shoulder or hip disarticulation the prosthesis must somehow be secured around the patient's pelvis/scapula. It is therefore difficult and cumbersome to reliably secure shoulder/hip disarticulation prostheses to patients.
For a hip disarticulation prosthesis, an exoprothesis having a hip joint, a knee joint, and an ankle joint should be provided. Typically a prosthetic device for hip disarticulation would have a large socket that receives and is affixed to the lower portion of the torso of the amputee, the socket being strapped around the patient's body. An example of a hip disarticulation prosthesis is described in U.S. Pat. No. 7,153,329 (Wilson). For a shoulder disarticulation prosthesis, an exoprosthesis having a shoulder joint, elbow joint and wrist joint should be provided. Typically a prosthetic device for a shoulder disarticulation would have a large socket that receives and is affixed to the shoulder area and is secured by strapping the socket around the patient's torso.
Such hip and shoulder disarticulation prostheses are uncomfortable to wear and use and suffer from numerous problems at the skin-socket interface. Focal points of increased stress caused by non-uniform pressure distribution can lead to skin-related complications, whilst the unnatural microbial environment generated in the socket is detrimental to the maintenance of healthy tissues. Furthermore, disarticulation exoprostheses are difficult to secure to a patient and can be unstable.
Even in transhumeral or transfemoral amputation, where the patient has a humeral or femoral stump to attach an external jointed limb prosthesis to, the patient will still have difficulty using the prosthesis as it is difficult for the patient to control and move the joint(s) of the external prosthesis.
Most jointed exoprostheses fall into two categories, these being body-powered prostheses and motor-actuated/myoelectric prostheses. A body-powered prosthesis is powered and controlled by gross body movements. For a prosthetic arm with an elbow joint and/or a gripping element (often a hook), these movements, usually of the shoulder, upper arm, or chest are captured by a harness system, which is attached to a cable that is connected to the exprosthesis, to control the prosthesis joint(s). However, such body-powered prostheses are not cosmetically pleasing and are difficult to control.
The myoelectric prosthesis is an external prosthesis that is linked to the residual musculature through an external electrode placed on the skin. These electrodes pick up the faint electrical signal produced by voluntary contractions of the residual muscles. This activates an electrically powered external prosthesis. However, the link is crude and the movements which can be produced are therefore relatively crude. Such prostheses are also heavy and difficult to use.